The mechanism of action of Ebselen differentiates between bacterial and mammalian thioredoxin reductase (TrxR). It displays fast oxidation of mammalian Trx and via the NADPH-TrxR catalyzed turnover of ebselen selenol with hydrogen peroxide, and therefore are mammalian antioxidants. Ebselen, and its diselenide, are strong competitive inhibitors of E. coli TrxR with K.sub.i of 0.14 .mu.M and 0.46 .mu.M, respectively. E. coli mutants lacking glutathione reductase or glutathione were much more sensitive to inhibition by ebselen. Since either glutaredoxin or thioredoxin systems are electron donors to ribonucleotide reductase, ebselen targets primarily glutathione and glutaredoxin-negative bacteria, a class which includes major pathogens. Ebselen, and similar compounds are therefore useful as antibacterial agents, even for multiresistant strains. Two major pathogenic bacteria, which previously had not been known to be sensitive to ebselen, Mycobacterium tuberculosis (tuberculosis) and Helicobacter pylori (stomach ulcer and cancer), were shown to be excellent targets. Helicobacter pylori was also sensitive to ebsulfur.

The crystal structure of 2-[(N,N-dimethylamino)methyl]benzenetellurenyl chloride (2), a compound previously formulated as bis [[2-(N,N-dimethylamino)methyl]phenyl] ditelluride bis hydrochloride (1a), was determinded. In the molecule 2, tellurium is bonded to the carbon of the phenyl group [2.120(3)Å], the nitrogen o fthe ortho dimethylamino substituent [2.362(3)Å], and the chlorine atom [2.536[1]Å]. There also is an intermolecular interaction of the tellurium atom with the phenyl ring of a neighbouring molecule [3.655(1)Å], resulting in the formation of zigzag chains along the b axis. The noncentorsymmetric space group of the crystal can be explained by the chiral surrounding of tellurium.

Primary- and secondary-alkyl aryl tellurides, prepared by arenetellurolate ring-opening of epoxides/O-allylation, were, found to undergo rapid (3-10 min) group-transfer cyclization to afford tetrahydrofuran derivatives in 60-74% yield when heated in a microwave cavity at 250C in ethylene glycol or at 180C in water. To go to completion, similar transformations had previously required extended photolysis in refluxing benzene containing a substantial amount of hexabutylditin. The only drawback of the microwave-assisted process was the loss in diastereoselectivity wich is a consequence of the higher reaction temperature. Substitution in the Te-aryl moiety of the secondary-alkyl aryl tellurides (4-OMe, 4-H, 4-CF3) did not affect the outcome of the group-transfer reaction in ethylene glycol. However, at lower temperature, using water as a solvent, the CF3 derivative failed to react. The microwave-assisted grouptransfer cyclization was extended to benzylic but not to primary- and secondary-alkyl phenyl selenides.

Triorganylsulfonium, -selenonium and -telluronium salts were reduced by carbon dioxide radical anions/solvated electrons produced in aqueous solution by radiolysis. The radical expulsion accompanying reduction occurred with the expected leaving group propensities (benzyl > secondary alkyl> primary alkyl> methy> phenyl), although greater than expected loss of the phenyl group was often observed. Diorganyl chalcogenides formed in the reductions were conveniently isolated by extraction with an organic solvent. Product yields based on the amount of reducing radicals obtained from the y-source were often higher than stoichiometric (up to 1800%) in the reduction of selenonium an dtelluronium compounds; it is likely that this result can be accounted for in terms of a chain reaction with carbon-centred radicals/formate serving as the chain transfer agent. The product distribution was essentially independent of the reducing species for diphenyl alkyl telluronium salts, whereas significant variations were seen for some of the corresponding selenonium salts. This would suggest the intermediacy of telluranyl radicals in the one-electron reduction of telluronium salts. However, pulse radiolysis experiments indicated that the lifetimes of such a species (the triphenyltelluranyl radical) would have to be less than 1 us.

Differential scanning calorimetry experiments with an unsaturated polyolester oil at 190˚C showed that an organotellurium compound in combination with a thiol or a sterically hindered phenol (BHT) could act in a synergistic fashion to protect the material form oxidation. Under more realistic conditions for an oil antioxidant (elevated temperature in the presence of oxygen, water and a copper coil; rotating pressure vessel oxidation test) the antioxidant protection offered by BHT itself at similar concentrations. In order for the novel antioxidant systems to become useful for protection of oils and fluids, more robust organotellurium compounds must be prepared.

An (RO)B3LYP/LANL2DZdp//B3LYP/LANL2DZ model for the prediction of the homolytic bond dissociation enthalpy (BDE) and adiabatic ionisation potential (IP) of phenolic antiocidants containing heavy chalcogens has been developed. The model has been used to probe the relationship between geometry, chalcogen substitution and activity for a series of a-tocopherol analogues of varying ring size. From this, a series of design principles for cyclic antioxidants has emerged, embodied by the compound 4-hydroxy-2,2,3,5,6-pentamethylbenzoselenete (4c). This compound is predicted to have a BDE comparable to a-tocopherol, and should act in a dual chain-breaking and hydroperoxide-decomposing manner, by analogy with other selenide antioxidants. The stability of chalcogen-substituted benzoxetes was considered, and the as yet unsynthesised benzotelluretes are predicted to be stable. Finally, an attempt was made to determine antioxidant mechanism by considering calculated BDE and IP data together with experimental rate data.

An approach to thyroid hormone analogues was proposed involving sequential substitution of cationic cyclopentadienyl(1.4-dichlorobenzene)iron(II) complexes with phenoxide/thiophenoxide and hydroxide/amine, followed by decomplexation. Although the selectivity for monosubstitution with phenolates and thiophenolates was poorer than previously observed, it was often possible to control the reaction with sterically less demanding phenolates of intermediate nucleophilicity. The subsequent introduction of a polar substituent into the monosubstituted product was successful with amine nucleophiles. A modified approach, based on the reverse order of substitution was also attempted. Whereas clean monosubstitution with hydroxide/hydroxide equivalents was unsuccessful, cyclopentadienyl(N-alkyl-1-chloro-4-aminobenzene)iron(II) complexes could be prepared in fair yields and further substituted with nucleophiles such as thiophenolates.

A new type of conjugated polymer, organoselenium substituted poly(p-pheylenevinylene) (PPV), was synthesized from the corresponding alkylselenenyl p-xylylene dibromide via a Gilch route using potassium tert-butoxide in THF. The p-xylylene dibromide precursors were synthesized by reacting lithiated bis(methoxymethyl)benzenes with elemental selenium, followed by alkylation of the generated selenolates. As a final demasking step, the bromomethyl functions were liberated by ether cleavage using boron tribromide. Bis-alkylselenenyl PPV was obtained with an average molecular weight Mw of approximately 300,000 g/mol and with polydispersity Mw/Mn=2. Due to low solubility, monoalkylselenenyl PPV was obtained with a considerably lower average molecular weight in the proximity of 16,000 g/mol and with a polydispersity slightly larger than 3. Absorption and flourescence spectroscopy revealed that the bis-alkylselenenyl PPV is extensively conjugated.